DE2724976A1 - SYNTHETIC SILICA - Google Patents

Description

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1A-49 271

Patent application

Applicant: RHONE- POULENC INDUSTRIES 22, avenus Montaigne 75 Paris (βέΊηβ), France

Title:

Synthetic silica

709849/1181

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Applicant: Rhßne-Poulenc Ind.

description

The invention relates to a new synthetic amorphous silica, a process for their production and their use in vulcanizates.

It has long been known as a substitute for the black fillers Incorporate silica as a reinforcing precipitate in elastomers, especially in tire manufacture.

In fact, by incorporating silica, good tensile strength can be achieved and a satisfactory grip of the tread of tires on damp or icy ground can be achieved · Unfortunately these good new properties are not achieved without disadvantages. For example, silica increases the heat build-up of the treads and reduces their abrasion resistance. With the help of coupling agents such as silanes, some of these Fix disadvantages; however, there are other disadvantages such as odor, scorch time and high production costs.

In order to ideally solve this problem, there is a need for a method of producing a silica which is used as a filler has all the advantages of the types of carbon black, but not their disadvantages.

An attempt was first made to find the results obtained with carbon black fillers to be transferred to the silicas. Above all, one has tried to establish a simple relationship between the specific Surface BET of the silica and its behavior in the vulcanizates.

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Thus, US Pat. No. 3,235,331 describes a process for the production of silica, which is used to reinforce elastomers, which leads to silicas with a BET surface area below 200 m ² / g.

US Pat. No. 3,445,189 shows that, on the basis of detailed investigations, a silica with good reinforcing properties for rubber a specific surface area in the range of

100 to 250 m / g and an oil absorption of more than 2 ml / g target.

US Pat. No. 2,731,326 attempts to establish a relationship under consideration the BET surface and the oil absorption. This document describes a silica in the form of Aggregates (primary structures) above the colloidal state, which have a specific surface area of 60 to 400 m / g and consists of spheroids of an amorphous and dense silica of substantially uniform particle size which are mutually exclusive fit and form open, networked structures or secondary structures; these structures are uniform with amorphous and dense silica reinforced and open in such a way that, after drying, its oil absorption number, given in ml / 100 g solid, 1 to 3 times the numerical value of the specific surface

specified in m / g.

According to this document, column 10, lines 66 to 73, must

a) the diameter of the finest spherical particles,

b) the packing density of the aggregates of the smallest particles in the cross-linked secondary structure,

c) the degree of reinforcement of this structure and

d) limits the uniformity or uniformity of the structure will.

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FR-PS 1 506 330 describes a process for the production of finely powdered silicas which are used as filler material serve primarily in rubber compounds and can have a BET specific surface area of up to 300 m / g, provided that they also have a roughness factor in the range of 2.5 to 3.5; the roughness factor is the ratio of the specific Surface BET denotes the surface determined by electron microscopy »

Attempts have also been made to establish a relationship between the water content of the filter cake during the manufacture of the silica and the behavior of the silicas in the rubber compounds, here a distinction was made between silicas with a high water content and Silicas with a lower water content are differentiated by the authors respectively as silicas with a high structure and silicas were designated with a lower structure.

From the prior art shown so far, the difficulties arise when one uses the silicas with the use of types of carbon black as reinforcing fillers for elastomers, especially in tire manufacture want to compare.

Two views must be taken into account here.

First of all, with Dannenberg and Cotten, in R.G.C.P., vol. 51, No. 5 - 1974 state that there is still no truly comprehensive Understanding of the processes involved in the reinforcement of elastomers and that there is still no general one There is agreement in this regard. According to another statement by the same authors, it is now generally recognized that the system of filler and reinforced elastomer and its mechanical properties to its behavior have to contribute.

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The second view is related to the observed differences in the behavior of carbon black fillers and silica fillers. These differences can be attributed, among other things, to differences in the morphology that exist between these two species of fillers are present and therefore the results obtained with one type of filler do not directly affect the other types of filler can be transferred. From this it can be explained, above all, that the starting from the specific surfaces and the oil absorption numbers, which are generally used to record the behavior of the carbon black fillers in the elastomer, The results presented can lead to contradicting results for silicas.

The oil number (DBP number) for carbon black fillers is in the range from 40 to 140 ml / 100 g, but can be up to 500 ml / 100 g for silicas. One could therefore assume that this Silicas have a strong reinforcing effect, but this is unfortunately not confirmed by the experiment. Furthermore was observed that silicas with very different specific Surface BET and oil absorption values are very similar Behavior as a reinforcing filler in rubber can develop.

The invention was based on the object of providing a new synthetic silica with improved filler properties. The solution to this problem was made taking into account the above considerations, one of which depends on the morphology the silica and the other based on the behavior of the silica fillers and with evidence of the influence the physico-chemical properties of the precipitated silicas on the mechanical, static and dynamic properties of the vulcanizates.

First of all, it was assumed that the relationships established so far, obviously sometimes deviating at least in part due to the different morphology of the

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Silica fillers can be returned to Russia. The types of soot, especially those used as fillers, generally have a high primary structure and a low secondary structure, while the secondary structure of silicas cannot be neglected in comparison with its primary structure.

The aggregates formed from the interconnected primary particles are referred to as the primary structure. The bonds between the primary particles in an aggregate are strong bonds of a chemical nature.The greater the number of primary particles per aggregate, the higher or stronger the primary structure _β. It must be pointed out that the number of primary particles per aggregate fluctuates a priori within wide limits can.

The secondary structure is the term used to describe the agglomerates to which the aggregates are aggregated as a result of physical interactions to have. In contrast to what goes on in the formation of the primary structure, these are physical bonds awake.

Furthermore, there was every reason to believe that the primary structure of the silica is different from that of the types of carbon black, more precisely that the number of elementary or primary particles, that form the aggregates is less than that of the types of soot,

The contradictions shown above with regard to the Ö3 numbers between types of soot and silicas could be explained by the fact that the oil number generally depends on the primary structure and the secondary structure of a filler depends on or reproduces this.

There is also the specific one determined by nitrogen adsorption Surface BET generally the outer surface (of the filler) and the surface of the micropores again. Now is just that

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The outer surface of the filler is accessible to the elastomer due to its dimensions; this explains that any relationship between the specific surface BET of the silicas and the mechanical properties of the vulcanizates is rather uncertain, while the reinforcing power of the soot types can easily be explained by this. One can still assume that one is relative can easily improve a static or theological property of a vulcanizate, for example, by adding a morphological Properties of the silica modified.

However, elastomers in particular, which are used for tires, have to meet very different requirements, for example breaking strength, flexural strength, elongation or heating or heating. In addition, there is the problem that the filler is well dispersed in the vulcanizate / and should have good adhesion to it.

According to the invention, a new silica has now been found or developed which serves primarily as a filler for elastomers and satisfactorily corresponds overall to the required theological, static and dynamic properties and can be satisfactorily distributed in the elastomers. This silica is characterized in that it has a CTAB surface area in the range from 80 to 125 m ² / g and a structure number of at least 0.80. Such a silica advantageously also has an oil absorption number in the range from 240 to 320 ml / 100 g, as well as a BET surface area in the range from 80 to 320 m 2 / g and a water content of the filter cake of 75 to 82 % and the BET ratio -Surface to CTAB surface is at least 1.1.

The measurements of the surface, the structure number and the oil absorption number have been carried out on the dry or returned product before any physical, mechanical, chemical or heat treatment has been carried out after drying, which would affect these values can.

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The measurements were carried out according to the following methods:

CTAB surface: outer surface by means of adsorption of Cethyltrimethylammoniumbromid at pH 9 according to the method of Jay, Janzen and G. Kraus in Rubber Chemistry and Technology 44 (1971), pp. 1287-1296.

The structure number is given by the inclination of the straight line which is obtained when the specific volume of the silica in ml / g is plotted in kg / cm2 as a function of the decadic logarithm of the pressure exerted on the silica, accordingly the procedure of A. Voet, W.N. Whitten in Rubber World, August 33-36 (1963).

The oil absorption number was determined by the absorption of dibutyl phthalate (DBP) determined according to ASTM D 281.

The BET surface area was determined using the Brunauer method, Emmett and Teller, described in The Journal of the American Chemical Society, Vol. 60, p. 309, February 1938.

To determine the water content of the filter cake, the slurry was placed on a Buchner filter under reduced pressure of 60 cm Hg filtered, the residue washed free of soluble salts with distilled water and the cake that remained dried at 105 ° C. The water content of the cow results from the ratio of the weight of the water removed to Weight of the filter cake.

Such a silica can in particular with the aid of a method can be obtained analogously to FR-PS 2 159 580, namely by allowing a strong acid to act on an alkali silicate, The rate of addition of the acid follows such a law that the change in the residual alkalinity of the medium is dependent remains practically constant over time. Given-

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271

if the addition of the acid can be interrupted at least once during a period of 5 to 20 minutes when the maximum formation of the polymers has been reached. The process according to the invention is further characterized in that one starts from a sodium silicate with a molar ratio SiO _{2 ZNa 2} O of 2 to ^, that the initial concentration of silicate in the medium is such that the silicate concentration given in SiO _{2 has} a value of 90 to 150 g / l SiO ₂ , based on the molar ratio SiO ₂ / Na ₂ O = 3.5; that furthermore the final concentration of SiO _{2 is} in the range from 60 to 90 g / l, that the total reaction time without including any interruptions made is 40 to 200 min and that a reaction temperature of 65 to 95 ^° C. is maintained.

It has surprisingly been found that the practical Carrying out the process in a simple Welse controlled by choosing a reaction temperature within the limits given above can be so that the water content of the cake is 75 to 82 wt .-%, i.e. 2.6 to 3.9 kg of water. per kg End product corresponds.

This relationship may be theoretically not yet be determined, but it was observed that _t in this range of conditions, an empirical relationship between the reaction temperature and the water content of the cake is.

In this way it becomes easy for those skilled in the art to complete the procedure to control or regulate. It is sufficient for this that, after observing all other conditions, a temperature within the given Range and the water content of the cake is determined. If this (water content) is not within the specified range Interval, the temperature only needs to be changed empirically in order to achieve the desired result.

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The other limit values were determined taking into account the requirements for the product and the requirements for large-scale process management. It has been observed that with an SiO ₂ content below 90 g / l the water content of the cake is too high to be able to carry out the process, and with an SiO ₂ content above 150 g / l the viscosity of the medium increases too much too, which makes it very difficult to carry out the process.

The same applies to the response time. If this is too short, kick the reactants are not in sufficient contact with one another; however, if it is too long, the CTAB surface is not big enough.

A particular and unexpected advantage of the method according to the invention lies in the simple control of the method in only one factor needs to be changed.

In practice, the acid is added according to a law after which the amount of acid added changes constantly. However, one can also use the equivalent means for this and the Gradually change the amount of acid added in successive periods of about 10 minutes.

or properties

Certain features / drying can also be improved: spray drying is preferably used in the process according to the invention. The invention also extends to application of the products according to the invention as reinforcing fillers for elastomers. So it can - fillers based on Silicic acid can be used according to the invention. These are fillers to be understood that the silica as such or after any physical, mechanical or chemical treatment.

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Examples

27 2 4 97G

The procedural measures for the manufacture of the silica are summarized in Table 1 below.

Examples 1 to 4 were carried out according to the invention. Example 1 explains a procedure in which the residual alkalinity of the medium remains constant over time. In Examples 2, 3 and 4, the addition of acid was interrupted more than once. In example 4 the product was dried in the oven, which resulted in somewhat lower values for the CTAB surface and the structure number leads.

In Example 5, the classic procedure with constant

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Acid feed in silicate complied with. In Example 6, the acid was added in the same way. However, temperature and time conditions were maintained such that the water content of the cake was within the values given for the product according to the invention. In Example 7, 54 l of water and then some silicate were initially introduced into a 200 l reactor up to pH 9.2. Then 67.2 1 sulfuric acid, d = 1.062 and 58.8 1 sodium silicate with a molar ratio Si0 ₂ / Na ₂ 0 = 3.5 and d = 1.240 were added at the same time with addition rates of 1080 ml / min and 1180 ml / min. After 50 minutes, the addition of silicate was interrupted and the addition of acid continued until the pH had dropped to 5. The final concentration of SiO ₂ was 76.8 g / l. The final product was spray dried.

In Examples 8 and 9, only the temperature conditions were outside of the procedure according to the invention; these two examples therefore show the importance of this factor.

In Table 2 below are the properties of the in these Examples of manufactured silicas listed.

Tables 1 and 2;

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Table 1

example capacity dNa ₂ O acid d silicate Na ₂ O im silicate of the reac
tors (1) (D H ₂ SO ₄ (D (g / l) 200 German 67.2 1.060 120 40 1 200 0.3 100 1.032 80 40 2 200 0.7 60 1.080 120 40 ^ 3 200 0.7 60 1.080 120 40 S 4 200
200 0.7 79.0
72.0 1.050
1.050 81.0
77.9 42,
47 OO
* - 5
co
^ 6 200 ** 9 Ξ7 200 53.2 1.080 122.4 38, ~ * 8 200 0.7 53.2 1.080 122.4 38, 5 9 0.7 , 5

SiO ₂ in the silicate (g / l)

135

135

135

135

145.3

159.5

113.5 113.5

the acid feed is constant, i.e. dNaoO / dt is variable simultaneous addition of the reactants

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Table 1 (cont.) Example temperature

Interruption while end Final concentrations Total time dry after min pH tration min min 0 SiO ₂ g / l O 10 VJl 90 121 atomization 20th 10 VJl 60 67 atomization 23 10 4.5 90 67 atomization 21 0 4.5 90 67 Oven at 105 ^° C 0 10 VJl 78.7 58 atomization 18th VJl 83 63 Oven at 105 ^° C 10 atomization 18th 10 5 79 67 atomization 21 5 79 67 atomization

80 83 83 83 76 90

100 55

Tabel

analysis

H ₂ O in the filter- kg H ₂ 0 / kg product cake, %

H ₂ O in the end product

pH of the final product

76

81.4

78.2

78.4

83.2

77

78.6

71

83

2.8 3.8

3.1 3.2

4.5

3.4

2.15

4.3 7.2

8.5
8.7
7.4
8.3
8.1
8.5
8.1
9

5.8

5.7

5.8

6.3

6.1

6.2

5.8

6.1

Table 2 (cont.)

analysis

1 2

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09

»7 8 9

surface surface Structure number oil number DBP BET CTAB ml / 100 g 240 80 0.90 260 305 122 1.00 318 290 102 1.00 290 305 92 0.85 294 275 164 0.90 370 310 75 0.70 258 217 149 0.93 320 330 60 0.695 200 340 145 1.05 325

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¹ A-49 271

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Subsequently, these silicas were used ± i Rubber compounds tested. The results relating to the enhancement ability are summarized in Tables 3 (a to c) below.

Three types of properties were tested for each silica:

First the theological properties, i.e. the minimum and maximum torque, the scorch time, the optimum time (optimum) and the rate of vulcanization.

The static properties, namely modulus at 300 % elongation, Shore hardness, elongation at break and breaking strength.

The dynamic properties: the heat build-up (accumulation), the dynamic * at 0 % _t 5 % and 100 % elongation and the viscose modulus at 5 % elongation.

The theological properties were determined according to the information in "Continuous Measurement of the Cure Rate of Rubber" - ASTM Special Technical Publication No. 383.

The static properties were determined according to the following standards (NF = French standard):

Breaking strength NF T 46 002

Test specimen A ₁

Elongation at break NF T 46 002

Test specimen A ₁

Shore hardness ASTM 676-58 T.

(immediate reading)

Module 300 % AFNOR NF T 46 002

Test specimen A ₁

♦ Young's modulus

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19 1A-49 271

30th ⁰ C 11 kg ο, 4 cm

The dynamic properties were prepared according to A. Voet and JC Morawski in Rubber Chemistry and Technology, 47 4 (1974) 758 - 777 and Compte Rendu de fin d ¹ etude ä la delegation genferale ä la Recherche Scientifique et Technique n ° 73-7 - 1151 determined.

The conditions for the experiment on the Goodrich flexometer were as follows:

Initial temperature of the chamber load amplitude

Finally, the following vulcanization mixture was used:

Parts by weight

Rubber SBR 1509 100.00

ZnO active 3.00

Stearic acid 1.00

Polyethylene glycol M - 4000 (PEG 4000) 2.40

Sulfur 2.30

Antioxidant (Permanax 49 HV) 2.00 4 _t 4'-bis (phe'nyl-isopropylidene) -diphenylamine

N-Cyclohexyl-2-benzothiazylsulfenamide (Rhodifax 16) 1.20

Benzothiazyl disulfide (MBTS) 1.20

Di-O-toluylguanidine (DOTG) 1.40

Tetramethylthiuram disulfide (DMTT) 0.20

Silica 40.00

The various minimum or maximum values that are required for a vulcanizate have to be required depend of course on this vulcanizate, in particular on the nature of the drawn or used elastomers. Therefore, the values given in line 10 of Table 3 are relative values that are only given by way of example. In the case of theological properties, no limit values were given because these are not standardized are, but only recommendations are available

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which, among other things, depend on the working conditions and are more satisfactory Way are distributed within the same area.

Tables 3 show that only the silicas according to the invention have a total of satisfactory properties exhibit.

In Example 6 and in Example 7, the reinforcing ability of the silica is insufficient, although the water content of the filter cake was satisfactory;

Example 7 illustrates that having proper oil uptake is insufficient for good reinforcing ability.

It is also known that silica must also be well dispersed. This state of dispersion was evaluated in the following manner:

There were several / um thick cuts of silica filler reinforced vulcanizate and then preferably the silicas stained with methyl red to make them visible under the optical microscope; the silica initially showed the same Refractive index like the elastomer.

The percentage dispersion is the percentage of silica that is dispersed in the form of conglomerates <8 / µm. That percentage was calculated as follows:

% Dispersion = 100 - j ^ -

of the remainder with X = total 17 / µm squares within / 10,000 squares

S = factor of surface swelling due to the effect of the Propellant,

ie S = surface of the section after swelling, surface of the section before swelling

L = 96% by volume SiO ₂ based on total rubber mass = weight SiO ₂ χ spec. Volume SiO ₂ 100 Weight of the mixture χ spec. Volume of the mixture

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The following ratings apply:

^ 98 % = good dispersion

95-9896 = mediocre dispersion

90-9596 = sufficient dispersion

«C9O96 = poor dispersion

The application of this test showed that the silica according to Example 1 gave a good dispersion value, while the dispersion value for the silica according to Example 5 was only mediocre.

The preceding examples were carried out using a vulcanizate based on an SBR rubber. Of course the fillers according to the invention can also be used in others Incorporate elastomers, for example into EPDM, polybutadiene, natural rubber, polyisoprene, etc.

Finally, the use of the fillers according to the invention is not restricted to their use as reinforcing fillers for elastomers limited.

Tables 3 (a to c)

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Table 3a

Example Moment Vulkanisa- optimal time Vulkanisationsge

speed min, s

1 9 87 3.30 6 2.30

I ^ 11 92 5.15 7.45 2.30

> S ¹⁰ 90 3.45 6.15 2.30

Z ** 6.5 86 4.45 7.45 3

87 rheological properties 92 Vulcanization
tion time
min, s optimal time
min, s moment
Minimum maximum 90 3.30 6th 9 5 86 5.15 7.45 11 5 85 3.45 6.15 10 87 4.45 7.45 6, 95 3.30 6.45 9, 91 2.45 5.45 9 95 4.30 7th 9 6.15 9 11 4.30 8th 9

3.15
3

7 9 95 4.30 7 2.30

8 11 91 6.15 9 2.54

9 9 95 4.30 8 2.30 10

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Table 3b static properties

Example module 300 % Shore hardness. Elongation at break breaking strength

% kg / cm

505 121

510 133

455 116

528 132 ^ _n ^

618 168

490 84

525 118

480 75

530 120

^ • 450 ^ 100 _λ

kg / cm ² 65 1 51 67 2 50 65 -i3 50 68
69
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* 1 6 46
36
41 65 »7 45 65 8th 43 66 9 45 Ϊ65 10 > 45

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Tabel

3c

Heat build-up
⁰ C Ε «Ο 96
10 " ⁸ dyn dynamic properties E '100 96
-8-2
10 "dyn cm E "5 96
10 ~ ⁷ dyn cm " ² IS) example 20th 1.15 E '50 96
-? -8th -?
cm ~ 10 dyn cm " 1.80 0.80 N) 1 21 1.50 1.00 1.50 1.05 CO 2 20.5 1.50 1.00 2.0 1.05 CD S 3 21 1.65 1.20 2.0 0.95 26th 2.00 1.10 1.60 1.65 Ϊ ³ 16.5 0.85 1.20 1.90 0.65 22nd 1.25 0.90 2.00 0.95 ü 7 19th 0.95 1.10 1.50 0.60 8th 22nd 1.40 0.80 2.00 1.00 9 ■ «21.5 1.15 Ϊ1.5 10

Claims (7)

Patent claims (1) Synthetic amorphous silica labeled 2 net with a CTAB surface from 00 to 125 m / g and a Structure number of at least 0.80. 2. Silica according to claim 1, characterized by an oil absorption number DBP of 240 to 320 ml / 100 g, a BET surface area from 80 to 320 m / g, the ratio of the BET surface area to CTAB surface area is equal to or greater than 1.1. 3. Silica according to claim 1 or 2, characterized by a burning loss of the filter cake of 75 to 82 %. 4. A method for producing the silica according to any one of claims 1 to 3 by allowing a strong acid to act on an alkali silicate solution, the acid being added to the alkali silicate solution at a variable rate so that the residual alkalinity of the medium remains essentially constant as a function of time and the addition of acid optionally being interrupted at least once during a period of 5 to 20 min when the maximum polymer formation is reached, characterized in that a sodium silicate with a molar ratio Si0 ₂ / Na ₂ 0 = 2 to 4 is used, an initial concentration of the Silicate in the medium of 90 to 150 g / l SiO ₂ , based on a molar ratio Si0 ₉ / Na ₅ 0 = 3 _f 5, that the final concentration of SiO _{2 is set} at 60 to 90 g / l ¹¹ a total reaction time of 40 up to 200 min, without taking into account any interruptions made, and a reaction ^{temperature of 65 to 95 0} C is maintained. 709849/1 18 ORIGHNAL INSPECTED 1A-49 271 5. The method according to claim 4, characterized in that that the reaction temperature is adjusted so that the water content of the cake is 2.6 to 3.9 kg of water per kg of end product is equivalent to. 6. The method according to claim 5, characterized in that that the acid is added in part to the silicate solution, keeping the feed rate constant for each proportion, but of changes from one part to the other and observes intervals of no more than 10 minutes for the addition time. 7. Use of the silica according to claim 1 to 3 as a reinforcing filler for elastomers. 7288 709849/1 181